Systems and methods for posterior dynamic stabilization of the spine

ABSTRACT

Devices, systems and methods for dynamically stabilizing the spine are provided. The devices include an expandable spacer or member having an unexpanded configuration and an expanded configuration, wherein the expandable member in an expanded configuration has a size, volume and/or shape configured for positioning between the spinous processes of adjacent vertebrae in order to distract the vertebrae relative to each other. The systems include one or more expandable members and an expansion medium for injection within or for filling the interior of the expandable member via the port. The methods involve the implantation of one or more devices or expandable spacers.

FIELD OF THE INVENTION

The present invention is directed towards the treatment of spinal disorders and pain. More particularly, the present invention is directed to systems and methods of treating the spine, which eliminate pain and enable spinal motion, which effectively mimics that of a normally functioning spine.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates a portion of the human spine having a superior vertebra 2 and an inferior vertebra 4, with an intervertebral disc 6 located in between the two vertebral bodies. The superior vertebra 2 has superior facet joints 8 a and 8 b, inferior facet joints 10 a and 10 b, posterior arch 16 and spinous process 18. Pedicles 3 a and 3 b interconnect the respective superior facet joints 8 a, 8 b to the vertebral body 2. Extending laterally from superior facet joints 8 a, 8 b are transverse processes 7 a and 7 b, respectively. Extending between each inferior facet joints 10 a and 10 b and the spinous process 18 are lamina 5 a and 5 b, respectively. Similarly, inferior vertebra 4 has superior facet joints 12 a and 12 b, superior pedicles 9 a and 9 b, transverse processes 11 a and 11 b, inferior facet joints 14 a and 14 b, lamina 15 a and 15 b, posterior arch 20, spinous process 22.

The superior vertebra with its inferior facets, the inferior vertebra with its superior facet joints, the intervertebral disc, and seven spinal ligaments (not shown) extending between the superior and inferior vertebrae together comprise a spinal motion segment or functional spine unit. Each spinal motion segment enables motion along three orthogonal axes, both in rotation and in translation. The various spinal motions are illustrated in FIGS. 2A-2C. In particular, FIG. 2A illustrates flexion and extension motions and axial loading, FIG. 2B illustrates lateral bending motion and FIG. 2C illustrated axial rotational motion. A normally functioning spinal motion segment provides physiological limits and stiffness in each rotational and translational direction to create a stable and strong column structure to support physiological loads.

Traumatic, inflammatory, metabolic, synovial, neoplastic and degenerative disorders of the spine can produce debilitating pain that can affect a spinal motion segment's ability to properly function. The specific location or source of spinal pain is most often an affected intervertebral disc or facet joint. Often, a disorder in one location or spinal component can lead to eventual deterioration or disorder, and ultimately, pain in the other.

Spine fusion (arthrodesis) is a procedure in which two or more adjacent vertebral bodies are fused together. It is one of the most common approaches to alleviating various types of spinal pain, particularly pain associated with one or more affected intervertebral discs. While spine fusion generally helps to eliminate certain types of pain, it has been shown to decrease function by limiting the range of motion for patients in flexion, extension, rotation and lateral bending. Furthermore, the fusion creates increased stresses on adjacent non-fused motion segments and accelerated degeneration of the motion segments. Additionally, pseudarthrosis (resulting from an incomplete or ineffective fusion) may not provide the expected pain-relief for the patient. Also, the device(s) used for fusion, whether artificial or biological, may migrate out of the fusion site creating significant new problems for the patient.

Various technologies and approaches have been developed to treat spinal pain without fusion in order to maintain or recreate the natural biomechanics of the spine. To this end, significant efforts are being made in the use of implantable artificial intervertebral discs. Artificial discs are intended to restore articulation between vertebral bodies so as to recreate the full range of motion normally allowed by the elastic properties of the natural disc. Unfortunately, the currently available artificial discs do not adequately address all of the mechanics of motion for the spinal column.

It has been found that the facet joints can also be a significant source of spinal disorders and debilitating pain. For example, a patient may suffer from arthritic facet joints, severe facet joint tropism, otherwise deformed facet joints, facet joint injuries, etc. These disorders lead to spinal stenosis, degenerative spondylolithesis, and/or isthmic spondylotlisthesis, pinching the nerves that extend between the affected vertebrae.

Current interventions for the treatment of facet joint disorders have not been found to provide completely successful results. Facetectomy (removal of the facet joints) may provide some pain relief; but as the facet joints help to support axial, torsional, and shear loads that act on the spinal column in addition to providing a sliding articulation and mechanism for load transmission, their removal inhibits natural spinal function. Laminectomy (removal of the lamina, including the spinal arch and the spinous process) may also provide pain relief associated with facet joint disorders; however, the spine is made less stable and subject to hypermobility. Problems with the facet joints can also complicate treatments associated with other portions of the spine. In fact, contraindications for disc replacement include arthritic facet joints, absent facet joints, severe facet joint tropism, or otherwise deformed facet joints due to the inability of the artificial disc (when used with compromised or missing facet joints) to properly restore the natural biomechanics of the spinal motion segment.

While various attempts have been made at facet joint replacement, they have been inadequate. This is due to the fact that prosthetic facet joints preserve existing bony structures and therefore do not address pathologies that affect facet joints themselves. Certain facet joint prostheses, such as those disclosed in U.S. Pat. No. 6,132,464, are intended to be supported on the lamina or the posterior arch. As the lamina is a very complex and highly variable anatomical structure, it is very difficult to design a prosthesis that provides reproducible positioning against the lamina to correctly locate the prosthetic facet joints. In addition, when facet joint replacement involves complete removal and replacement of the natural facet joint, as disclosed in U.S. Pat. No. 6,579,319, the prosthesis is unlikely to endure the loads and cycling experienced by the vertebra. Thus, the facet joint replacement may be subject to long-term displacement. Furthermore, when facet joint disorders are accompanied by disease or trauma to other structures of a vertebra (such as the lamina, spinous process, and/or transverse processes) facet joint replacement is insufficient to treat the problem(s).

Most recently, surgical-based technologies, referred to as “dynamic posterior stabilization,” have been developed to address spinal pain resulting from more than one disorder, when more than one structure of the spine have been compromised. An objective of such technologies is to provide the support of fusion-based implants while maximizing the natural biomechanics of the spine. Dynamic posterior stabilization systems typically fall into one of two general categories: posterior pedicle screw-based systems and interspinous spacers.

Examples of pedicle screw-based systems are disclosed in U.S. Pat. Nos. 5,015,247, 5,484,437, 5,489,308, 5,609,636 and 5,658,337, 5,741,253, 6,080,155, 6,096,038, 6,264,656 and 6,270,498. These types of systems involve the use of screws that are positioned in the vertebral body through the pedicle. Certain types of these pedicle screw-based systems may be used to augment compromised facet joints, while others require removal of the spinous process and/or the facet joints for implantation. One such system, the Zimmer Spine Dynesys® employs a cord which is extended between the pedicle screws and a fairly rigid spacer which is passed over the cord and positioned between the screws. While this system is able to provide load sharing and restoration of disc height, because it is so rigid, it does not effective in preserving the natural motion of the spinal segment into which it is implanted. Other pedicle screw-based systems employ articulating joints between the pedicle screws. Because these types of systems require the use of pedicle screws, implantation of the systems are often more invasive to implant than interspinous spacers.

Where the level of disability or pain to the affected spinal motion segments is not that severe or where the condition, such as an injury, is not chronic, the use of interspinous spacers are preferred over pedicle based systems as they require a less invasive implantation approach and less dissection of the surrounding tissue and ligaments. Examples of interspinous spacers are disclosed in U.S. Pat. No. Re. 36,211, U.S. Pat. Nos. 5,645,599, 6,695,842, 6,716,245 and 6,761,720. The spacers, which are made of either a hard or compliant material, are placed between adjacent spinous processes. The harder material spacers are fixed in place by means of the opposing force caused by distracting the affected spinal segment and/or by use of keels that anchor into the spinous process. The more compliant or flexible spacers employ artificial ligaments that are wrapped around the spinous processes of the vertebrae above and below the level where the spacer is implanted. While slightly less invasive than the procedure required for implanting a pedicle screw-based dynamic stabilization system, the implantation of interspinous spacers still require muscle and supraspinous and interspinous ligament dissection.

With the limitations of current spine stabilization technologies, there is clearly a need for an improved means and method for dynamic posterior stabilization of the spine that address the drawbacks of prior devices. In particular, it would be highly beneficial to have a dynamic stabilization system that involves a minimally invasive implantation procedure, where the extent of distraction between the affected vertebrae is adjustable upon implantation and at a later time if necessary. It would be additionally advantageous if the system or device was also removable in a minimally invasive manner.

SUMMARY OF THE INVENTION

The present invention provides devices, systems and methods for stabilizing at least one spinal motion segment. The devices include an expandable spacer or member having an unexpanded configuration and an expanded configuration, wherein the expandable member in an expanded configuration has a size, volume and/or shape configured for positioning between the spinous processes of adjacent vertebrae in order to distract the vertebrae relative to each other. The expandable member may be balloon made of either non-compliant or compliant material, or may include a mesh material which may be coated or lined with a non-porous material. The device may further include a port for coupling to a source of an inflation and/or expansion medium for inflating and/or expanding the expandable member. In certain embodiments, the port may be used to deflate or evacuate the expandable member. The devices may further include one or more tabs for anchoring the expandable member to the spinous processes. Optionally, the device may include one marker on a surface of the expandable member to facilitate fluoroscopic imaging.

The invention further includes systems for stabilizing at least one spinal motion segment which include one or more expandable members and an expansion medium for injection within or for filling the interior of the expandable member via the port. The subject systems may further include at least one means for anchoring or securing the expandable member to the spinal motion segment.

The invention further includes methods for stabilizing at least one spinal motion segment which involve the implantation of one or more devices or expandable spacers of the present invention, in which the expandable member is positioned between the spinous processes of adjacent vertebrae in an unexpanded condition and then subsequently expanded to a size and/or shape for selectively distracting the adjacent vertebrae. The invention also contemplates the temporary implantation of the subject devices which may be subsequently removed from the patient once the intended treatment is complete. Many of the methods involve the percutaneous implantation of the subject devices.

These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures:

FIG. 1 illustrated s perspective view of a portion of the human spine having two vertebral segments.

FIGS. 2A, 2B and 2C illustrate left side, dorsal and top views, respectively, of the spinal segments of FIG. 1A under going various motions.

FIG. 3A illustrates an interspinous device of the present invention in an unexpanded or collapsed state coupled to a cannula of the delivery system of the present invention. FIG. 3B is an enlarged view of the interspinous device of FIG. 3A.

FIG. 4A illustrates an interspinous device of the present invention in an expanded state coupled to a cannula of the delivery system of the present invention. FIG. 4B is an enlarged view of the interspinous device of FIG. 4A.

FIGS. 5A-5C illustrates top, dorsal and side views of an initial step of the method of the present invention in which a cannula is delivered to the target implant site.

FIGS. 6A and 5B illustrate dorsal and side views of the step of dissecting an opening within the spinous ligament utilizing a cutting instrument of the system of FIGS. 3 and 4. FIG. 6C is an enlarged view of the target area within the spinous ligament.

FIGS. 7A and 7B illustrate dorsal aid side views of the step of inserting the interspinous device of FIG. 4A into the dissected opening of the spinous ligament. FIGS. 7C and 7D are enlarged views of the target area in FIGS. 7A and 7B, respectively.

FIGS. 8A and 8B illustrate dorsal aid side views of the step of inflating or expanding the interspinous device of FIG. 4A within the implant site. FIGS. 8C and 8D are enlarged views of the target area in FIGS. 8C and 8D, respectively.

FIG. 9A illustrates a side view of the step of filling the interspinous device of FIG. 4A with an expansion medium. FIG. 9B is an enlarged view of the target area in FIG. 9A.

FIG. 10A illustrates a dorsal view of the step of further securing the interspinous device of FIG. 4A within the implant site. FIG. 10B is an enlarged view of the target area in FIG. 10A.

FIGS. 11A and 11B illustrate dorsal aid side views of the step of inserting another embodiment of an interspinous device into the dissected opening of the spinous ligament.

FIGS. 11C and 11D are enlarged views of the target area in FIGS. 11A and 11B, respectively.

FIGS. 12A and 12B illustrate dorsal aid side views of the step of expanding the interspinous device of FIGS. 11A-11D within the implant site. FIGS. 12C and 12D are enlarged views of the target area in FIGS. 12A and 12B, respectively.

FIG. 13A illustrates a side view of the step of filling the interspinous device of FIGS. 11A-11D with an expansion medium. FIG. 131B is an enlarged view of the target area in FIG. 13A.

DETAILED DESCRIPTION OF THE INVENTION

Before the subject devices, systems and methods are described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a spinal segment” may include a plurality of such spinal segments and reference to “the screw” includes reference to one or more screw and equivalents thereof known to those skilled in the art, and so forth.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

The present invention will now be described in greater detail by way of the following description of exemplary embodiments and variations of the devices and methods of the present invention. The invention generally includes an interspinous spacer device as well as instruments for the percutaneous implantation of the interspinous spacer. A key feature of the interspinous spacer device is that it is expandable from a low profile configuration to a higher profile or operative configuration. This design allows the device, when in the low profile condition, to be delivered by percutaneous means without requiring the removal of any portion of the spinal motion segment into which the device is implanted.

Referring now to the drawings and to FIGS. 3 and 4 in particular, an exemplary interspinous spacer device 24 of the present invention is illustrated in collapsed and expanded configurations, respectively. Interspinous device 24 includes an expandable spacer body 4 that has a size and shape when in the expanded condition for operative positioning between the spinous processes of adjacent superior and inferior vertebrae of the spinal motion segment being treated. Expandable body 34 is made of an expandable or inflatable biocompatible material such as non-porous material, e.g., latex, acrylate or a metal mesh, e.g., a nitinol or titanium cage.

Those spacers made of an inflatable non-porous material, i.e., balloon type spacers (see FIGS. 3-10), are inflated with an inflation or expansion medium, such as air, saline, another biologically compatible fluid, or a flowable solid material, such as polyurethane, or a gel, which thickens or hardens substantially upon injection into balloon 34. In one embodiment, balloon 34 is initially inflated with air to provide some structure or rigidity to it to facilitate its optimum positioning and alignment between the spinous processes. Once positioned as desired, balloon 34 is injected with a flowable solid material (the air therein being displaced possibly via a vent hole within port 32). In certain embodiments, the expandable body is made of a non-compliant or semi-compliant material so as to maintain a substantially fixed shape or configuration and ensure proper, long-term retention within the implant site. In other embodiments, the expandable member may be made of a compliant material. In any embodiment, the compressibility and flexibility of balloon 34 can be selected to address the indications being treated.

Other embodiments of the subject spacers are made of an expandable mesh or cage (see FIGS. 11-12). The mesh or cage maybe made of a super-elastic memory material which is compressible for delivery through a cannula and which is self-expanding upon implantation. Upon expansion, the mesh or cage may be self-retaining whereby its struts, links or wires are sufficiently rigid by themselves to maintain the expanded condition and withstand the natural forces exerted on it by spine. The mesh or cage may have an exterior coating or an interior lining made of materials similar to or the same as that used for the balloon spacers, or may otherwise be embedded in such material. In certain embodiments, an expansion medium may be used to fill the interior of the cage or mesh structure, such as with a biologically compatible fluid or flowable solid material used with the balloon-type embodiments.

In certain embodiments of present invention, either during the implant procedure or in a subsequent procedure, the size or volume of the implanted expandable spacer may be selectively adjusted or varied. For example, after an initial assessment upon implant, it may be necessary to adjust, either reduce or increase, the size or volume of the spacer to optimize the intended treatment. Further, it may be intended to only temporarily implant the spacer for the purpose of treating a temporary condition, e.g., an injured or bulging or herniated disk. Once the repair is achieved or the treatment completed, the spacer may be removed, either with or without substantially reducing the size or volume of the spacer. In other embodiments, the spacer as well as the inflation/expansion material may be made of biodegradable materials wherein the spacer degrades after a time in which the injury is healed or the treatment completed.

When unexpanded or deflated, as shown in FIGS. 3A and 3B (balloon type) and in FIGS. 11C and 11D (mesh type) expandable body 34 has a low profile, such as a narrow, elongated shape, to be easily translated through a delivery cannula 70. The shape of expandable body 34, when in an expanded or inflated state, has larger profile which is generally H-shaped. Expandable body 34 has lateral or side portions 30, end portions 26 and apexes 28 defined between the side portions 30 and the end portions 26. End portions 26 are preferably recessed or contoured to provide a narrowed central portion along the height dimension or major axis of expandable body 34 to readily fit between and to conform to the spinous processes. Accordingly, expandable body 34 has an apex-to-apex dimension (i.e., height or major axis dimension) from about 3 to about 5 cm and a width dimension (minor axis dimension) from about 2 to about 4 cm

For those embodiments of expandable bodies which comprise a balloon configuration, balloon 34 has an inflation or injection port 32 at a sidewall 30 for coupling to a source of inflation or expansion material or medium. Port 32 may consist of a one-way valve which is self-sealing upon release from an inflation mechanism or tube 76. Port 32 is further configured to releasably engage from tube 76, where such engagement may be threaded or involve a releasable locking mechanism. Where the expandable body comprises a mesh or cage, port 32 simply acts as an exit port, however, where an expansion material is used, it also functions as an injection port for the expansion material.

Optionally, device 24 may include a pair of tabs 36 which may be positioned on one side of the device where the tabs 36 are preferably situated at the apexes 28 of expandable body 34. Pins or screws (not yet shown) may be used to secure the tabs against the spinous process to further ensure long-term retention of device 24 within the implant site. Tabs 36 are made of a biocompatible material, such as latex, acrylate, rubber, or a metal, and may be made of the same material used for the expandable member 34. Shown here attached to tabs 36 are tethers 38 which are used in part to manipulate the positioning of expandable body 34 upon implantation into the targeted spinal motion segment. The tethers may be made of any suitable material including but not limited to materials used to make conventional sutures. They may also be made of a biodegradable material. While two tabs and associated tethers are provided in the illustrated embodiment, one, three or more may be employed, where the respective tabs are located on the expandable body so as to be adjacent a bony structure of the vertebra suitable for anchoring thereto. In embodiments which do not employ securing tabs 36, tethers 38 may be attached directly to the expandable body itself.

Optionally still, device 24 may further include radiopaque markers 40 on the surface of expandable body 34 visible under fluoroscopic imaging to facilitate positioning of the expandable body. Any number of markers 40 may be employed anywhere on expandable body 34, however, as few as four markers, one at each apex, may be sufficient. With embodiments employing cage or mesh expandable bodies, the cage or mesh material itself may be radiopaque.

A system of the present invention includes a cannula device 70 having an outer sheath 72, a proximal hub 78 and preferably at least two interior lumens 74, 76 for the percutaneous delivery the device and other tools for implanting the device, which tools may include a cutting instrument 62 (see FIG. 6C), a device delivery instrument 76, an endoscope, etc., which tools will be further discussed in the context of the description of the subject methods with reference to FIGS. 5-10.

In FIGS. 5A-5C, the spinal motion segment of FIG. 1 is illustrated having spinal ligament 54 extending between the superior spinous process 18 and the inferior spinous process 22. A percutaenous puncture is made into the skin 30 adjacent the target spinal motion segment of a patient undergoing the implantation of the interspinous device of the present invention, and a cannula 70 is penetrated to the spinous ligament 54. The puncture and subsequent penetration may be made by way of a sharp distal tip of cannula 70 or by a trocar (not shown) delivered through a lumen of cannula 70.

As illustrated in FIGS. 6A-6C, the spinous ligament 54 is then dissected and an opening 58 created therein by way of a cutting instrument 60, such as a simple scalpel, an electrosurgical device or the like, delivered through a lumen of cannula 70. Cutting instrument 60 may then be removed from cannula 70 and, as illustrated in FIGS. 7A-7D (balloon type) and in FIGS. 11A-11D (cage type), a delivery instrument 16 having interspinous device 24 operatively preloaded is delivered through cannula 70.

The preloading of device 24 to delivery instrument 76 involves providing expandable body 34 in an unexpanded or deflated state and releasably coupled, as described above, by way of inflation or injection port 32 of expandable body 34 to the distal end of delivery instrument 76. In addition to functioning as a pusher, instrument 76 may act as an inflation lumen for balloon type embodiments through which an inflation medium is transported to within expandable body 34.

Depending upon the material used to fabricate expandable body 34, the expandable body may have a degree of stiffness in an unexpanded or deflated state such that it may maintain an elongated configuration so as to be directly insertable and pushable through cannula 70. This may the case where the expandable member 34 is made of a cage or mesh material. Alternatively, a pusher or small diameter rod (not shown) may be inserted through inflation port 32 to within expandable body 34 to keep it in an elongated state so as to prevent expandable body 4 from bunching within cannula 70 and to provide some rigidity to more effectively position the expandable body in the target implant site. The rod is then removed from expandable body 34 and from delivery device 76 upon positioning the expandable body at the target implant site. In either case, expandable body 34 is folded or compressed about its minor axis with the side wall opposite the inflation port 32 defining a distal end 25 (see FIG. 3B) and the apexes 28 of the expandable body folded proximally of distal end 25 to provide a streamline, low profile configuration for delivery through cannula 70.

Once interspinous device 24 is preloaded to delivery device 76 as just described, device 24 is then inserted into a lumen of cannula 70 with tethers 38 pulled back and trail proximally so that the tether ends 38 a extend from hub 78 of cannula 70. Expandable body member 34 is translated through cannula 70 to within opening 58 within spinous ligament 54 as best illustrated in FIGS. 7C and 11C. For best results, expandable body 34 is centrally positioned within opening 58 so that the countered ends 26 of expandable body 34 readily engage with the opposed spinous processes 18, 22. Fluoroscopy may be employed to visualize markers 40 so as to ensure that expandable body 34 centrally straddles the spinous ligament opening 58, i.e., the markers on the distal side 25 of the expandable body are positioned on one side of the spine and the markers on the proximal side of the expandable body (the side on which port 32 is located) are positioned on the other side of the spine.

Once centrally positioned, expandable body 34 is inflated or expanded, as illustrated in FIGS. 8A-8D and 12A-12D. For balloon spacers, inflation occurs by allowing an inflation or expansion medium, as discussed above, to enter into the interior of the expandable body via port 32. For expandable mesh spacers, the expandable body may be configured to expand automatically upon exiting cannula 70. The inflation or expansion of expandable body 34 may also be visualized under fluoroscopy whereby markers 40, as best shown in FIG. 8C, are observed and the position of expandable body 34 may be adjusted to ensure optimum positioning upon complete inflation. Adjustments of the expandable body's position may be accomplished by manually pulling on one or both tether ends 38 a which in turn pulls on tabs 26 to which the tethers 38 are attached at their proximal ends. The tethers 38 are selectively pulled as necessary to center or optimally position interspinous expandable body 34 to achieve the desired treatment of the targeted spinal motion segment.

With embodiments in which the expandable body is initially inflated with air and then filled with a solid or fluid medium, the latter is preferably not delivered or injected into the interior of the expandable body until the position of the expandable body within the interspinous space has been verified and optimized. This is beneficial in situations where, upon inflation, it is found that the expandable body is misaligned within the interspinous space and requires repositioning. The expandable body may simply be deflated of air to the extent necessary and repositioned in a less inflated or deflated state. If necessary, for example where it is found that the maximum spacer or expandable body size is insufficient for the particular application at hand, expandable body 34 may be completely deflated and removed and replaced with a more suitably sized unit.

For balloon spacers and those mesh spacers which are not by themselves sufficiently self-retaining, once the position and extent of inflation or expansion of expandable body 34 are optimized, the expansion medium, e.g., polyurethane, is allowed to flow or injected into the interior of the expandable body via port 32. As illustrated in FIGS. 9A and 9B, expandable body 34 is caused to expand to a selected volume and in so doing forces apart (see arrow 80) the spinous processes 18, 22 in between which it is situated. This selective distraction of the spinous processes also results in distraction of the vertebral bodies 2, 4 (see arrow 82) which in turn allows the disk, if bulging or distended, to retract to a more natural position (see arrow 84). Again, the extent of distraction or lordosis undergone by the subject vertebrae can be monitored by observing expandable body markers 40 under fluoroscopy.

The extent of possible distraction maybe limited by the capacity of expandable body 34 and the type of expandable body material employed. In certain embodiments, such as expandable bodies made of non-compliant or semi-compliant balloons, the requisite volume of the inflation medium may be substantially fixed whereby the balloon achieves its fully expanded configuration upon filling it with the fixed volume of medium. In other embodiments, such as with balloons made of a compliant material, the extent of expansion may be variable and selectable intraoperatively depending on the extent of lordosis or distraction to be achieved between the spinous processes in which balloon 34 is now interposed.

Upon achieving the desired distraction between the vertebrae, inflation/expansion lumen 76 is disengaged from expandable body port 32 which then becomes sealed by means of a one-way valve that is closed upon disengagement of lumen 76. Inflation/expansion lumen is then removed from cannula 70. While the opposing compressive force exerted on expandable body 34 by the distracted spinous processes 18, 22 may be sufficient to permanently retain expandable body 34 therebetween, the interspinous device may be further secured to the spinous processes 18, 22 to ensure that the expandable body does not slip or migrate from its implanted position. To this end, tabs 36 are anchored to the spinous processes as illustrated in FIGS. 10A and 10B and in FIGS. 13A and 13B. Any type of anchoring means, such as screws, tacks, staples, adhesive, etc. may be employed to anchor tabs 36. Here, cannulated screws 90 are used as anchors and are delivered to the target site releasably coupled to screw driving instrument 88. While various screw attachment and release mechanisms may be employed, a simple configuration involves providing the screws 90 with a threaded inner lumen which is threadably engagable with the threaded distal end of instrument 88.

To ensure accurate placement of screws 90, along with instrument 88, can be tracked and translated over respective tethers 38, which function as guide wires. By manipulating instrument 88, the screws are driven or screwed into the respective spinous process. Screwdriver 88 is then disengaged or unscrewed from screw 90. After both tabs 36 are securely anchored to the spinous processes, the screwdriver and the cannula may be removed from the patient's back.

While certain of the expandable spacers are intended to be permanently implanted within a spine, certain others may be implanted only temporarily to facilitate the healing of an injury or the treatment of a reversible or non-chronic condition, such as a herniated disk. For such temporary treatments, the expansion material most likely is a fluid, such as saline, which may be easily aspirated through port 32 or may be allowed to drain out via a penetration or cut made in the expandable member. In those embodiments in which the expansion material is a flowable solid, which may or may not subsequently harden within the expandable member, the material may be one that is reconstitutable into a liquid form which may then be subsequently aspirated or evacuated from the expandable member. For percutaneous removal of the expandable member, a cannula such as cannula 70 may be used and an aspiration instrument delivered therethrough and coupled to port 32. After deflation and/or evacuation of the expandable member, and removal of the tacks, sutures, staples, etc. if such are used to secure tabs 36, the expandable member may be easily removed through cannula 70. With biodegradable spacers, removal of the spacer is obviated.

It should be noted that any of the above-described steps or procedures, including but not limited to cannulation of the target area, dissection of the spinous ligament, insertion of the expandable body within the dissected opening of the spinous ligament, inflation and/or expansion of the expandable body, adjustment or readjustment of the expandable body, and anchoring of the tabs, etc., may be facilitated by way of a scope 62 delivered through a lumen of cannula 70 to the open distal tip of cannula 70. Alternatively, a second cannula delivered through another percutaneous penetration may be employed for use of an endoscope and any other instruments needed to facilitate the procedure.

The subject devices and systems may be provided in the form of a kit which includes at least one interspinous device of the present invention. A plurality of such devices may be provided where the devices have the same or varying sizes and shapes and are made of the same or varying materials. The kits may further include instruments and tools for implanting the subject devices, including but not limited to, a cannula, a trocar, a scope, a device delivery/inflation/expansion lumen, a cutting instrument, a screw driver, etc., as well as a selection of screws or other devices for anchoring the spacer tabs to the spinous processes. The kits may also include a supply of the expandable body inflation and/or expansion medium. Instructions for implanting the interspinous spacers and using the above-described instrumentation may also be provided with the kits.

The preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims. 

1. An interspinous device for stabilizing at least one spinal motion segment comprising a first vertebra having a first spinous process and a second vertebra having a second spinous process, the device comprising: an expandable member having an unexpanded configuration and an expanded configuration, wherein the expandable member in an expanded configuration has a size and shape configured for positioning between and providing distraction of the first and second spinous processes.
 2. The device of claim 1, wherein the expandable member is a non-compliant balloon.
 3. The device of claim 1, wherein the expandable member is a compliant balloon.
 4. The device of claim 1, wherein the expandable member comprises a mesh material.
 5. The device of claim 4, wherein the mesh material is coated with a non-porous material.
 6. The device of claim 1, wherein the expandable member has a substantially H-shaped configuration.
 7. The device of claim 1, wherein the expandable member comprises polyurethane.
 8. The device of claim 1, further comprising at least one tab for anchoring the expandable member to the spinous processes.
 9. The device of claim 8, further comprising a tether attached to the at least one tab.
 10. The device of claim 1, further comprising at least one tether attached to the expandable member.
 11. The device of claim 1, wherein the expandable member has a port for coupling to a source of an expansion medium.
 12. The device of claim 1, wherein the port comprises a one-way valve mechanism.
 13. The device of claim 1, wherein the expandable member is inflatable.
 14. The device of claim 1, further comprising an expansion medium contained within the interior of the expandable member when in an expanded configuration.
 15. The device of claim 1, further comprising at least one marker on a surface of the expandable member.
 16. A system for stabilizing at least one spinal motion segment comprising a first vertebra having a first spinous process and a second vertebra having a second spinous process, the system comprising: an expandable member having an unexpanded configuration and an expanded configuration, wherein the expandable member in an expanded configuration has a size and shape configured for positioning between and providing distraction of the first and second spinous processes, wherein the expandable member has a port; and an expansion medium fillable within the interior of the expandable member via the port.
 17. The system of claim 16, further comprising at least one anchor for securing the expandable member to the spinal motion segment.
 18. The system of claim 17, wherein the at least one anchor is a screw configured for securing the expandable member to a spinous process.
 19. The system of claim 16, wherein the expansion medium comprises polyurethane.
 20. A kit for stabilizing at least one spinal motion segment comprising a first vertebra having a first spinous process and a second vertebra having a second spinous process wherein a spinous ligament extends between the first and second spinous processes, the kit comprising: at least one expandable member having an unexpanded configuration and an expanded configuration, wherein the at least one expandable member in an expanded configuration has a size and shape configured for positioning between and providing distraction of the first and second spinous processes; and a cannula configured for percutaneous delivery to a target site within the spinal motion segment wherein the expandable member is deliverable through the cannula when in an unexpanded configuration.
 21. The kit of claim 20, further comprising instructions for implanting the expandable member between the first and second spinous processes.
 22. A method for stabilizing at least one spinal motion segment comprising a superior vertebra and an inferior vertebra, the method comprising: providing the device of claim 1; forming an opening in the spinous ligament; positioning the expandable member within the opening wherein the expandable member is in the unexpanded configuration; and expanding the expandable member to the expanded configuration wherein the first and second vertebrae are distracted a selected distance.
 23. The method of claim 22, wherein the expanding comprises inflating the expandable member with air.
 24. The method of claim 23, the expanding further comprises filling the expandable member with a flowable medium.
 25. The method of claim 22, wherein the steps of forming, positioning and expanding are performed through a percutaneous penetration in the patient's skin.
 26. The method of claim 25, wherein the steps of forming, positioning and expanding are performed through a cannula positioned within the percutaneous penetration.
 27. The method of claim 22, further comprising anchoring the expandable member to one or both of the spinous processes.
 28. The method of claim 22, wherein the expandable member has a volume in the expanded configuration, the method further comprising adjusting the volume of the expandable member.
 29. The method of claim D7, further comprising reducing the volume of the expandable member and removing the expandable member subsequent to reducing the volume.
 30. A method for stabilizing at least one spinal motion segment comprising a superior vertebra and an inferior vertebra, the method comprising: forming an opening in the spinous ligament; positioning an expandable member within the opening wherein the expandable member is in an unexpanded configuration; and selectively expanding the expandable member to an expanded configuration wherein the first and second vertebrae are distracted a selected distance. 